Linkage mechanism for supercharger system

ABSTRACT

Disclosed is an induction or supercharger system (16) for a piston engine (10) having a Roots type blower (14) for supercharging an air-fuel mixture from a carburetor (12) having primary and secondary throttle valves (64) and (66). The induction system defines a naturally aspirated flow path, a recirculation flow path, and a supercharger flow path. The flow paths are controlled by valves (18) and (20). Valves (18, 64 and 66) are moved between their respective opened and closed positions by a linkage mechanism (44) including a lever (72) and linkage assemblies (74) and (76). The linkage assemblies include resilient means (88) and (102) which respectively move the throttle valves open and the valve (18) closed. Valve (20) is opened in response to a differential pressure across the naturally aspirated flow path and the supercharger flow path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. 214,301,filed Dec. 8, 1980 now U.S. Pat. No. 4,364,366; application Ser. No.214,304, filed Dec. 8, 1980 and to U.S. patent application Ser. No.214,358, filed Dec. 8, 1980 now U.S. Pat. No. 4,364,367. All of theseapplications are assigned to the assignee of this application.

FIELD OF THE INVENTION

This application relates to supercharger systems and more specificallyto a linkage mechanism for a supercharger system selectively operable inboth a naturally aspirated mode and in a supercharged mode.

BACKGROUND OF THE INVENTION

During the last several years increasing cost and reduced availabilityof fuel has motivated many automobile manufacturers to produce more fuelefficient vehicles by not only reducing vehicle weight but by alsoreducing engine power relative to vehicle weight, thereby deprivingmotorists of accustomed vehicle performance, such as power foracceleration, hill climbing, etc. To regain the acceleration and hillclimbing power and still retain fuel efficiency many automotivemanufacturers have offered or considered offering vehicles withsupercharger systems having displacement or turbodynamic blowers whichare either mechanically driven by the engine crankshaft or turbinedriven by the engine exhaust gases. Such systems though well-known havenot met with great acceptance even though they had been satisfactorilyused for years to maintain aircraft engine power with increasingaltitude and to increase racing car speeds. Most of the automobilesuperchargers have been of the turbine driven-turbodynamic blower typecommonly referred to as turbochargers, a few have been of themechanically driven-displacement blower types, e.g., vane or Rootsblowers V-belt driven by the engine crankshaft.

The turbochargers in automobiles have been disappointing for severalreasons. They have been relatively inefficient when operated outside oftheir range of maximum efficiency, have had slow response, have requiredrelatively complicated and expensive controls to prevent over boost andengine damage, and have required large hot ducts in the already crampedand overheated engine compartments to direct exhaust gases to and fromthe turbine. Of these, the most unacceptable is probably slow responsein boosting engine power for accelerating the vehicle from zero or lowspeeds.

The supercharger systems with mechanically driven displacement typeblowers in automobiles have also been disappointing for several reasons.When used to deliver air to the engine full time over the full operatingrange of the engine, they have also been relatively inefficient and havecaused rough low speed engine operation. When used in combination with abypass duct to deliver naturally aspirated air to the engine at lowengine engine speeds and/or low engine power settings to improve roughlow-speed engine operation, they have also been relatively inefficientand have had either slow response, as with turbochargers, or have had anoverly fast response which causes a stepwise increase in engine powerand therefore cause jerky vehicle operation. Further, superchargersystems with displacement type blowers have been subject to catastrophicfailure due to engine backfire unless provided with special blowoutvalves.

SUMMARY OF THE INVENTION

An object of the invention is to provide an efficient induction systemfor a supercharged engine.

Another object of the invention is to provide a supercharger inductionsystem having a linkage mechanism which readily controls the pressure ofsupercharged air in response to engine power demand.

According to a feature of the invention an induction system includes aninlet and an outlet respectively adapted to receive air and deliver theair to an expansible combustion chamber of an engine; first and secondair flow paths connected in parallel between the inlet and outlet; asupercharger interposed in the second path; and an improved valve meansincluding a valving member and means responsive to differential pressurebetween the inlet and outlet, the valving member being movable betweenfirst and second positions to control air flow in the first path forregulating the differential pressure between minimum and a maximumpressures, and the pressure responsive means is operative to move thevalving member toward the first position to decrease the differentialpressure in response to the differential pressure exceeding the maximumpressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The supercharger system of the instant invention is shown in theaccompanying drawings in which:

FIG. 1 is a side elevational view of the supercharger system mounted ona partially shown engine;

FIG. 2 is an end elevational view of the system looking in the directionof an arrow 2 in FIG. 1; and

FIGS. 3 and 4 are cross sectional views of the system looking along line3--3 of FIG. 1.

Certain terminology referring to proposed environment, direction, andmotion will be used in the following description. This terminology isfor convenience and clarity in describing the invention and should notbe considered limiting in the appended claims unless the claims areexplicitly so limited.

DETAILED DESCRIPTION OF THE DRAWINGS

Looking first at FIGS. 1-4 in general, therein is disclosed a partiallyshown engine 10 equiped with a carburetor 12, a supercharger 14, and aninduction or supercharger system 16. The induction system includes avalve 18 (see FIGS. 3 and 4) operative in its full open position of FIG.3 to direct the flow of an air-fuel mixture from the carburetor to theengine via a first or natural aspiration path and to direct dischargeair from the supercharger outlet back to the supercharger inlet via arecirculation path. Valve 18 is operative in its fully closed positionto block the recirculation path and direct the supercharged air-fuelmixture from the supercharger outlet to the engine via a valve 20 whichis spring biased to its closed position.

Carburetor 12 may be a single point fuel injector and is preferablydisposed upstream of the supercharger as shown herein. However,carburetor 12 may be positioned downstream of the supercharger and maybe deleted in lieu of multiple fuel injector nozzles which may injectfuel either into the manifold or directly into the expansible chambersof the engine. Further, engine 10 is preferably an Otto cycle engine ofthe type used in automotive and truck type vehicles. However, the enginemay be of the diesel cycle type, in which case carburetor 12 would bereplaced by fuel injection nozzles which inject fuel directly into theexpansible chambers. Herein, engine 10 is a conventional four-cylinder,four-stroke, spark-ignited engine wherein each cylinder defines anexpansible chamber having inlet and outlet ports controlled by poppetvalves which are actuated by a camshaft driven by a crankshaft; none ofthese components are shown since they do not form part of the instantinvention and since they are well-known. Portions of the engine, whichare shown, include a valve cover 22, a head assembly 24, a blockassembly 26, an air filter 28, and a crankshaft driven shaft 30 having aV-pulley 32 fixed thereto.

Supercharger 14, which may be a turbine driven variable or positivedisplacement blower, is preferably a mechanically driven positivedisplacement blower. Herein, the supercharger is a Roots type blowerhaving two unshown rotors with three helical lobes each. The rotors aredriven by a shaft 34 having a V-pulley 36 fixed thereto and mechanicallyconnected to V-pulley 32 via a V-belt 38. Hence, the fluid or air-fuelmixture displacement of the supercharger is in direct proportion toengine speed.

Supercharger 14 is also preferably of the type which does not compressfluid being displaced by the blower until the fluid reaches the bloweroutlet, that is, the displaced air is compressed only when the pressurein the region of the blower outlet is elevated. Roots blowers are ofthis type and are substantially more efficient when operating in arecirculation mode than blowers which compress fluid prior todisplacement of the fluid at the blower outlet. For example, when valve18 is open, the supercharger outlet is connected to the superchargerinlet via the recirculation path. Hence, when in the recirculation mode,the supercharger will only absorb the amount of energy necessary tocirculate the fluid, since the supercharger inlet and outlet pressuresare substantially the same. If the supercharger were of the type whichcompresses fluid prior to displacement at its outlet, the superchargerwould further absorb the energy necessary to compress the fluid, whichenergy would then be mostly wasted when the fluid is displaced into therecirculation path.

A Roots type blower is further preferred when induction system 16 isused with an Otto cycle engine, since the adiabatic efficiency of such ablower is relatively high in the 1.0 to 1.5 pressure ratios normallyused with Otto cycle engines. To further save energy either of theV-pulleys 32 or 36 could be replaced by a clutch mechanism, e.g., amagnetic clutch such as disclosed in U.S. Pat. No. 3,494,453. Suchclutches are well-known and it should suffice herein to say that theclutch could be automatically controlled in response to engine operatingparameters, one such parameter could be throttle position and/or theclutch could be controlled by a manually operated switch.

Looking now at induction system 16 in a more specific manner, the systemincludes an intake manifold assembly 40 fixed to head assembly 24 by aplurality of bolts 42 and a linkage mechanism 44 which is only partiallyshown in FIG. 1. Manifold assembly 40 includes duct assemblies 46 and 48and supercharger inlet and outlet ducts 50 and 52. The duct assembliesand ducts may be attached to each other in any of several conventionalways, e.g., welding, clamping, and/or bolted flanges. Herein the lowerend 48a of duct assembly 48 is welded to duct assembly 46, one end 50aof supercharger inlet duct 50 is welded to duct assembly 48 and one end52a of supercharger outlet duct 52 is flange mounted to duct assembly46. The other ends 50b and 52b of ducts 50 and 52 are flange mounted tothe supercharger inlet and outlet, respectively, as best seen in FIG. 1.Manifold assembly 40 is shown herein substantially as it was fabricatedfor a prototype of the supercharger system. It is contemplated that theassembly will be made substantially smaller and more compact in actualproduction to reduce the system bulk, passage length, and passagevolume.

Looking mainly at FIGS. 3 and 4, duct assembly 46 includes chambers 46aand 46b, which are separated by the valve 20, and four passages whichextend diagonally from chamber 46a to the unshown poppet valvecontrolled inlets of the four expansible chambers of engine 10. Two ofthe four diagonal passages 46c and 46d are visible in FIGS. 3 and 4.Compartment 46a is in continuous communication with a passage 48bdefined by the exterior walls of duct assembly 48 and a partition 48c.Compartment 46b is in continuous communications with a passage 52cdefined by supercharger outlet duct 52 and with a passage 48d defined bythe exterior walls of duct assembly 48 and partition 48c.

Valve 20, which is also visible in the broken away portion of FIG. 1,includes flapper type valving members 20a and 20b which pivot about ahinge pin 54 supported by a rectangular frame member 56. Frame 56 alsofunctions as the valve seat for the flappers which are biased toward theseat or closed position by a torsion spring 58. Spring 58 maintains theflappers in their closed position of FIGS. 1 and 3 when the fluidpressure in compartments 46a and 46b is substantially the same. Thefluid pressure in compartments 46a and 46b or the difference in fluidpressure is controlled by valve 18. As valve 18 moves from its openposition of FIGS. 1 and 3 toward its closed position of FIG. 4 the fluidpressure difference begins to increase, whereby the flappers are movedby the differential pressure to their open position of FIG. 4.

The flow of air-fuel mixture in passages 48b and 48d is controlled byvalve 18. Valve 18 includes a butterfly type valving member 60 whichpivots about the axis of a shaft 62 rotatably supported by the walls ofduct assembly 48. One end of shaft 62 extends through one of the wallsand is visible in FIGS. 1 and 2. As may be seen in FIG. 4, valvingmember 60 cooperates with a valve seat defined by the lobes projectingfrom the walls of duct assembly 48. Valving member 60 is provided withunequal surface areas 60a and 60b on opposite sides of its pivotal axisand is moved from the open position to the closed position in responseto counterclockwise rotation of shaft 62, as viewed in FIGS. 2 and 3.

The upper portion of duct assembly 48 above valve 18 defines a chamberor passage 48e which is in continuous communication with a passage 50cdefined by supercharger inlet duct 50. Passage 48e receives an air-fuelmixture from carburetor 12 by way of primary and secondary throats 12aand 12b which are controlled by primary and secondary throttle valves 64and 66. Carburetor 12 and throttle valves 64 and 66 in particular formpart of the power control means. The throats receive ambient air throughfilter 28 which is not shown in FIGS. 3 and 4. Fuel is mixed with theair in a conventional manner as the air passes through the throats. Theamount of air passing through the throats is controlled by the throttlevalves in conjunction with the rotational speed of the engine. Thevalves are respectively fixed to shafts 68 and 70 which are rotatablysupported by the carburetor walls. One end of each shaft extends througha wall of the carburetor. Shaft 68 is visible in FIG. 1 and both shaftsare visible in FIG. 2. The throttle valves 64 and 66 are respectivelyrotated clockwise and counterclockwise from their substantially closedpositions of FIG. 3 to their full open positions of FIG. 4.

In brief, induction system 16, as mentioned in the first paragraph ofthe detailed description, defines a first or naturally aspiratedair-fuel flow path, a second or supercharged air-fuel flow path, and arecirculation air-fuel flow path. The first path is defined by passage48e, the left side of valve 18, passage 48b, chamber 46a, and thediagonal passages connecting chamber 46a with the expansible chamberinlets. The second path is defined by passage 48e, passage 50c,supercharger 14, passage 52c, chamber 46b, valve 20, chamber 46a, andthe diagonal passages. The recirculation path is defined by passage 52c,chamber 46b, passage 48d, the right side of valve 18, and passages 48eand 50c.

Looking now at linkage mechanism 44, as best seen in FIG. 2, themechanism in conjunction with throttle valves 64 and 66, butterfly valve18, and flapper valve 20 forms the power control means for engine 10.Mechanism 44 includes a pivotal lever 72 and linkage assemblies 74 and76 connected in parallel for respectively controlling the throttlevalves and the butterfly valve. Lever 72 includes an opening 72a forattachment of a control rod or cable moved by an accelerator pedal of avehicle, an opening 72b for attachment of an unshown pivot support fixedto the engine, an opening 72c pivotally attached to a collar 78 oflinkage assembly 76, and an opening 72d pivotally attached to a collar80 of linkage assembly 74.

Linkage assembly 74 includes the collar 80 slidably mounted on a rod 82,stop rings 84 and 86 fixed to the rod, a helical compression spring 88positioned between collar 80 and stop ring 84, an L-shaped bell crank 90fixed to shaft 68 of the primary throttle valve 64 and pivotallyattached to rod 82, and a lever 92 fixed to shaft 70 of the secondarythrottle valve. Lever 92 is connected to bell crank 90 via a lost motionconnection including a pin 94 fixed to lever 92 and projecting into anarcuate opening 90a defined by bell crank 90. Opening 90a has a radiusof curvature centered on the axis of shaft 68.

Linkage assembly 76 includes the collar 78 slidably mounted on a rod 96,stop rings 98 and 100 fixed to the rod, a helical compression spring 102positioned between stop ring 98 and collar 78, and a lever 104 fixed atone end to shaft 62 of the butterfly valve and pivotally attached at theother end to rod 96.

OPERATION

Assume now that engine 10 is installed in a vehicle having an automatictransmission wherein about ninety percent of the accelerator pedalmovement fully opens the carburetor throttle valves and the remainder ofthe accelerator pedal movement downshifts the transmission into apassing or lower speed ratio gear when the transmission is in high gearand the vehicle speed is less than some predetermined amount. Alsoassume that depression of the accelerator pedal applies a rightwardlydirected force to attachment point 72a of lever 72 and that an unshownspring applies a leftwardly directed force to attachment point 72a forreturning lever 72 to its idle or minimum power position of FIG. 2 whenthe accelerator pedal is released. As may be seen in FIG. 2, arightwardly directed force applied to attachment point 72a rotates lever72 clockwise about attachment point 72b and applies a leftwardlydirected force to collars 78 and 80 of the linkage assemblies forresiliently moving bell crank 82 via spring 88 and rod 82 and forresiliently moving lever 104 via spring 102 and rod 96. Lever 72 andlinkage assemblies 74 and 76, which are not drawn to exact scale, arearranged such that about fifty percent of full clockwise rotation oflever 72 from its minimum power position of FIG. 2 effects simultaneousopening and closing rotation, respectively, of primary throttle valve 64and butterfly valving member 60 while secondary throttle valve 66remains closed. This intermediate or fifty percent position of lever 72rotates primary throttle valve 64 about seventy-five percent of its fulltravel from its substantially closed position of FIG. 3 toward its fullopen or vertical position of FIG. 4. In this position throttle valve 64is substantially full open since there is little increase in air flowthrough throat 12a solely in response to additional opening movement ofthe throttle value. The intermediate or fifty percent position of lever72 rotates butterfly valving member 60 of valve 18 to a positionsufficiently close to its closed position to effect a slight pressuredifference across the valving member, i.e., the pressure in passage 48dbecomes slightly greater than the pressure in passage 48e since thisvalving member position slightly restricts the flow of naturallyaspirated air-fuel mixture to passage 48b and slightly restricts theflow of recirculation air-fuel mixture in passage 48d from thesupercharger outlet back to the supercharger inlet. Hence, in about thefifty percent position of pivotal lever 72, engine 10 is still operatingbasically in the naturally apsirated mode, i.e., suction from theexpansible chambers is still providing vertically all of the force formoving the air-fuel mixture through the induction system to the engine.The slight pressure difference also acts across valve 20 and applies anopening force to flappers 20a and 20b which negates or balances theclosing force of torsion spring 58, whereby the flappers thereafterprogressively moved from their closed positions toward their openpositions as the pressure difference increases in response to additionalclosing movement of valving member 60 by lever 72 through linkageassembly 76.

With lever 72 in about the fifty percent position, spring 102 modulatesthe position of valving member 60 in combination with the difference insurface areas 60a and 60b to maintain the slight pressure differencerelatively constant substantially independent of minor variations inengine speed. For example, if the engine load increases with lever 72fixed at the fifty percent position, the engine speed will decrease andso will the amount of air-fuel mixture flowing in the induction system.Hence, the slight pressure difference across valving member 60 will tendto decrease, thereby decreasing the counter or feedback force to spring102 due to the surface area difference of valving member 60 and therebyallowing the resilient force of spring 102 to move the valving membertoward its closed position enough to maintain the slight pressuredifference relatively constant. If the engine load decreases with lever72 again fixed at the fifty percent position, the engine speed willincrease and so will the amount of air-fuel mixture flowing in theinduction system. Hence, the slight pressure difference across valvingmember 60 will tend to increase, whereby the feedback force increasesand moves the valving member towards its open position against spring102 to maintain the slight pressure difference relatively constant. Thedifference in surface area of valving member 60 and the resilient forceof spring 102 allows the engine to operate substantially in thenaturally aspirated mode over a relatively large speed range when lever72 is near or at its fifty percent position of full travel.

As previously mentioned, the first fifty percent movement of lever 72rotates bell crank 90 clockwise. This amount of rotation takes up thelost motion provided by arcuate opening 90a. Continued clockwiserotation of bell crank 90, due to further rotation of lever 72, effectsa counterclockwise rotation of secondary throttle valve shift 70,thereby moving the secondary throttle valve towards its full openposition while simultaneously moving primary throttle valve 64 furthertowards its vertical or fully open position and while simultaneouslyrotating butterfly valving member 60 further towards its fully closedposition. At about the ninety percent position of lever 72 the primaryand secondary throttle valves are fully open and the butterfly valvingmember 60 is fully closed. When in this position the power control meansand lever 72, which is part of the power control means, are in themaximum power position. Further movement of lever 72 is absorbed bysprings 88 and 102, thereby allowing the accelerator pedal to actuate atransmission downshift mechanism, not shown.

During movement of lever 72 from the fifty percent position to theninety percent position, the resilient forces applied by spring 102progressively increase to move butterfly valving member 60 to its fullyclosed position, thereby progressively blocking the naturally aspiratedand recirulation paths and allowing the pressure of the air-fuel mixturein the supercharger path to progressively increase from about zeropounds per square inch gauge to about six pounds per square inch gaugeas both a function of the position of lever 72 and the rotational speedof engine 10. During this period of pressure increase, the flappers ofvalve 20 move from their closed to their fully open positions. Hence, avehicle operator by simple manipulation of the accelerator pedal cansmoothly transition from the natually aspirated or unboosted mode ofoperation to a full boost mode of operation by progressively depressingthe accelerator pedal or he can modulate the boost pressure at anypartial amount needed for any particular driving situation. Further,since valving member 60 is resiliently moved from its first position toits second position, any abnormally high pressures in passage 48b, suchas backfire pressures, will act on the unequal areas 60a and 60b andforce valving member 60 towards its first position against the resilientforce of spring 102. Hence, valving member 60 in combination with spring102 provides the dual function of modulating boost pressure and thesafety function of protecting against catastrophic failure due to enginebackfire through the induction system.

The induction system as disclosed herein provides engine 10 with arelatively efficient naturally aspirated flow path for medium and lowengine power settings, smooth transition to and from the superchargerflow path, and when needed an almost instantaneous boost in superchargerpressure to its maximum boost (which herein by way of example is sixpounds per square inch gauge) even at relatively low engine speeds.Further, since linkage assemblies 74 and 76 are connected in parallelfrom lever 72 to their respective valves, the amount of movement of therespective valves in response to a given amount of accelerator pedalmovement may be readily varied independent of each other by merelyvarying the position of openings 72a, 72b, 72c, and 72d with respect toeach other. Additionally, since the linkage assemblies are in parallelan optimum spring rate or rates may be selected to control valve 18 vialinkage assembly 76 without affecting the operation of the throttlevalves by linkage assembly 74. Hence, the linkage assemblies of linkagemechanism 44 may be readily adapted to fit a great variety of vehicleswhich in turn may have a variety of operating demands requiring a shiftin the transition points between natural aspiration, partialsupercharging, and full supercharging.

A preferred embodiment of the invention has been disclosed forillustrative purposes. Many variations and modifications of thepreferred embodiment are believed to be within the spirit of theinvention. For example, carburetor 12 could be provided with onlyprimary throttle valves or a single throttle valve; in which case thesystem may transition to the supercharger path prior to or after thethrottle valve or valves have fully opened. The following claims areintended to cover the inventive portions of the preferred embodiment andvariations and modifications believed to be within the spirit of theinvention.

What is claimed is:
 1. In an induction system including an inletreceiving air, an outlet adapted to deliver the air to an expansiblecombustion chamber of an engine, first and second air flow pathsconnected in parallel between the inlet and outlet, a superchargerinterposed in the second path; the improvement comprising:valve meansincluding a valving member and means responsive to differential pressurebetween the inlet and outlet, said valving member moveable between openand closed positions to control air flow in said first path forregulating said differential pressure between a minimum and a maximumpressure, and said pressure responsive means operative to move saidvalving member toward said first position to decrease said differentialpressure in response to said outlet pressure exceeding said maximumpressure.
 2. The system of claim 1, wherein said valving member and saidpressure responsive means comprises:a butterfly valving member havingunequal surface areas with respect to its pivotal axis.
 3. The system ofclaim 1, wherein said valving member and said pressure responsive meanscomprises a butterfly valving member having unequal surface areas withrespect to its pivotal axis, and further including:resilient means formoving said valving member for said open position to said closedposition.
 4. The system of claim 1, 2, or 3, wherein said superchargercomprises:a positive displacement supercharger adapted to bemechanically driven by the engine.
 5. The system of claim 1, 2, or 3,wherein said valving member is operative in said open position to allowflow from the inlet to the outlet via said first path and is operativein said closed position to block flow from the inlet to the outlet viathe first path.
 6. In an engine of the type including an expansiblecombustion chamber; an induction manifold having an inlet receiving anair-fuel mixture via a throttle valve controlled by a power controlmeans having means selectively moveable between minimum and maximumengine power positions, an outlet delivering the air-fuel mixture to thechamber, and first and second air fuel mixture flow paths connected inparallel between the inlet and outlet; and a supercharger interposed inthe second path for pumping the air-fuel mixture from the inlet to theoutlet; the improvement comprising:valve means including a valvingmember and means responsive to differential pressure between the inletand outlet, said valving member moveable between open and closedpositions to control flow in said first path in response to movement ofthe selectively moveable means between the minimum and maximum positionsfor respectively regulating said differential pressure between a minimumand a maximum, and said pressure responsive means operative to move saidvalving member toward said first position to decrease said outletpressure in response to said differential pressure exceeding saidmaximum.
 7. The system of claim 6, further including:resilient meansinterposed between the selectively moveable means and said valvingmember for moving said valving member from said open position to saidclosed position.
 8. The system of claim 6, wherein said valving memberand said pressure responsive means comprises:a butterfly valving memberhaving unequal surface areas with respect to its pivotal axis.
 9. Thesystem of claim 6, wherein said valving member and said pressureresponsive means comprises a butterfly valving member having unequalsurface areas with respect to its pivotal axis and furtherincluding:resilient means interposed between the selectively moveablemeans and said valving member for moving said valving member from saidopen position to said closed position.
 10. The system of claim 6, 7, 8,or 9, wherein said supercharger comprises:a positive displacementsupercharger mechanically driven by the engine.
 11. The system of claim6, 7, 8, or 9, wherein said valving member is operative in said openposition to allow flow from said inlet to said outlet via said firstpath and is operative in said closed position to block air flow fromsaid inlet to said outlet via said first path.
 12. In an engine of thetype including an expansible combustion chamber, a supercharger havingan inlet and an outlet, first and second air flow paths connected inparallel, the first path to deliver unsupercharged air to the chamber,the second path to deliver air to the supercharger inlet and from thesupercharger outlet to the chamber, and power control means having meansselectively moveable between minimum and maximum engine power positions,the improvement comprising:valve means including a valving member andmeans responsive to pressure, said valving member moveable between afirst position respectively allowing and substantially blocking air flowto the combustion chamber via the first and second paths and a secondposition respectively allowing and blocking air flow to the combustionchamber via said second and first paths, and said pressure responsivemeans for biasing said valving member toward said first position inresponse to predetermined pressure differences between portions of saidfirst and second paths; and a linkage means including means forresiliently moving said valving member from said first position to saidsecond position in response to movement of said selectively movablemeans from said minimum to said maximum position.
 13. The engine ofclaim 12, wherein said power control means includes a throttle valve andfurther including:second linkage means for moving said throttle valvefrom a substantially closed position towards a substantially openposition in response to movement of said selectively moveable means fromsaid minimum power position to an intermediate power position.
 14. Theengine of claim 12, wherein the air pressure in said portions of saidfirst and second paths is substantially the same when said valvingmember is in said first position, said pressure difference begins toincrease as said valving member approaches said second position, saidsecond linkage means resiliently moves said throttle valve to asubstantially full open position as said pressure differences begin toincrease, and said resilient means of said first linkage meansresiliently moves said valving member to said second position inresponse to movement of said selectively moveable means to said saidmaximum power position.
 15. The engine of claim 12, wherein said powercontrol means includes a carburetor disposed in a common air inlet pathportion of said first and second paths and said moveable means is athrottle valve disposed in said carburetor, and further including:secondlinkage means for moving said throttle valve from a substantially closedposition to a substantially full open position in response to movment ofsaid selectively moveable means from said minimum power position to anintermediate power position.
 16. The engine of claim 12, wherein saidpower control means includes a carburetor disposed in a common air inletpath portion of said first and second paths and said moveable meansincludes a primary and a secondary throttle valve disposed in saidcarburetor and interconnected by a lost motion means, and furtherincluding:second linkage means for moving said primary throttle valvefrom a substantially closed position to a substantially full openposition in response to movement of said selectively moveable means fromsaid minimum power position to an intermediate power position andthereafter moving said primary throttle valve to a full open positionand said secondary throttle valve from a substantially closed positionto a full open position in response to further movement of saidselectively moveable means toward said maximum power position.
 17. Theengine of claim 16, wherein the air pressure in said portion of saidfirst and second paths is substantially the same when said valvingmember is in said first position, said pressure difference begins toincrease as said valving member approaches said second position, saidsecond linkage means moves said primary throttle valve to saidsubstantially full open position as said pressure difference begins toincrease and thereafter moves said primary throttle valve to said fullopen position while moving said secondary throttle valve to said openposition in response to further movement of said selectively moveablemeans toward said maximum power position.
 18. The engine of claim 12,wherein said valving member is closed when in said second position andwherein said resilient means applies a force to move said valving membersufficiently close to said closed position to effect a slight pressuredrop thereacross in response to movement of said selectively moveablemeans to an intermediate position between said minimum and maximumengine power positions.
 19. The engine of claim 18, wherein saidresilient means applies an increasing force for moving said valvingmember closed in response to further movement of said selectivelymoveable means from said intermediate position toward said maximumposition.
 20. The engine of claim 12, 18, or 19 wherein said resilientmeans applies a force to said valving member substantially equal to acounterforce applied to said valving member when said selectivelymoveable means is in said maximum engine power position.
 21. In a systemadapted to supply combustion air to an inlet of an expansible combustionchamber of an engine having a supercharger to boost the pressure of theair; the system including a manifold assembly defining first and secondair flow paths for respectively directing unboosted and boosted air tothe chamber inlet, the first path having an unboosted air inlet and anoutlet communicating with the chamber inlet, the second path having anair inlet and outlet communicating respectively with upstream anddownstream portions of said first path, and the second path inlet andoutlet adapted to be interposed by the supercharger; the improvementcomprising:a butterfly valving member disposed in the first path betweenthe second path inlet and outlet and moveable between open and closedpositions respectively allowing and blocking air flow thereacross, saidbutterfly valving member having unequal surface areas with respect toits pivotal axis to assist opening movement of said valving member.